This is the first nationwide study aimed to evaluate in-hospital mortality and comorbidities of extremely low birth weight (ELBW) infants in Thailand between 2015–2020. Data of ELBW infants were collected from the National Health Coverage Scheme. The incidence of ELBW Thai infants was 1.75 per 1000 live births. Sixty-five percent of ELBW infants were delivered in tertiary-care facilities, with 63% surviving until discharge. In-hospital mortality was 36.9%. Non-invasive respiratory supports were documented in just 17.6% of the study population, whereas total parenteral nutrition was used in 52.3% of neonates. There were several comorbidities, with the three most frequent including respiratory distress syndrome (70.7%), neonatal jaundice (66.7%), and sepsis (60.4%). The median hospitalization cost for one ELBW infant who survived was 296,438.40 baht ($8719). Conclusion: Thailand had an acceptable ELBW infant survival rate (63%), but comorbidities remained particularly severe and cost one hundred times the median hospital cost for one ELBW infant that survived in comparison to a normal newborn infant. Better health outcomes require strategies to raise awareness of the issues and the appropriate implementation of evidence-based solutions, particularly improving neonatal care facilities, as well as early referral of high-risk pregnant women and neonates, which will aid in the future reduction of neonatal morbidities and mortalities.